Mar 282018
 


Have you ever been confused about what is in a garden product? Here’s a prime example!

For many years, peat moss and sphagnum moss have been staple components of potting mixes and a useful addition to garden beds. More recently, however, a number of concerns have been raised about their use – harm to irreplaceable environments, increased carbon emissions and more. But working out what you are actually getting when you buy a product with ‘peat’ or ‘sphagnum’ in the name can be tricky. Let’s try to unravel the story.
Both sphagnum moss and peat moss are used in gardens as soil amendments for a number of reasons:

  • their low pH means that they are useful for camellias, azaleas and other acid loving plants,
  • they can hold water up to 20 x their weight,
  • they generally lack weed seeds and pathogens,
  • their ability to easily absorb and release some mineral ions,
  • their high porosity allows penetration of fine roots.

They are especially valued for growing mushrooms and for the air layering method of plant propagation.

What are They?

Peat is formed from decomposition of sphagnum moss and other organisms over many thousand years. There are more than 370 species of sphagnum which may form peat which accumulates in cool, moist climates in wetlands or lakes which turn into bogs.  It is mainly found in the northern hemisphere – Canada, northern Russia, Scandinavia and Scotland – and, in the southern hemisphere, in New Zealand, Tasmania, Argentina and Chile.  Small areas occur in south-Eastern Australia between 300 and 1500 metres altitude.

Peat bogs and wetlands are fragile ecosystems occurring only where moisture conditions are right and, therefore, host a unique variety of fauna and flora.

Peat and sphagnum moss are harvested by mining either by machinery or, traditionally, by hand. Networks of ditches are dug so that water drains out. The bog then dries out and the moss dies. Surface vegetation is removed and the upper layers allowed to dry in the sun before being vacuum harvested or removed by other methods.  Peat/moss is put into large bales and removed from the site either by vehicles or by being dragged.

Peat has also been harvested for use as fuel, particularly in the northern hemisphere, contributing to peat bog destruction. In Finland, for example, only 40% of peat lands remain.

What are the Environmental Consequences of Peat and Sphagnum Moss Harvesting?

Change and Loss of Fragile Habitats

Moss may start regenerating, but very slowly, if at all, since the ditches and vehicular movement have changed the pattern of water flows so that conditions are no longer suitable for moss growth. This allows other vegetation, such as sedges, to invade the site displacing the indigenous species.

Methane and Carbon Dioxide Release

Changes in water flows which direct water away from the bogs are perhaps the most dangerous result of peat harvest since they also cause extensive drying of the peat with accompanying release of methane.  Lightening strikes can ignite it and sometimes auto-ignition occurs when other flammable gases are present.  The results are huge underground fires which may burn for many weeks, as occurred Indonesia and Spain, releasing large amounts of carbon dioxide1– something our planet does NOT need to happen.  Currently a peat bog in south western Victoria is burning.  The resultant ash cloud and other gases released are endangering the health of nearby residents.

“Resource” Depletion

Continued formation of peat is threatened by global warming, as well as extensive mining, since drying out of the top layer kills the sphagnum moss layer above the decomposing material.   Because it takes such a long time for peat to form, mining it means depleting an almost non-renewable resource.

Conservation Measures

In Australia, peat lands are given varying degrees of protection, ranging from threatened in Tasmania to endangered under the Environment Protection and Biodiversity Conservation Act 1999 for the whole of the country, Victoria and relevant parts of NSW.

Sustainable Harvesting?

Listing of sphagnum moss as endangered in Tasmania means that controlled harvesting is permitted.  A Code of Practice sets out clear conditions which exclude a number of sites and include maintaining at least 30% cover. 2

Garden Products for Sale

This is where much confusion lies.  In North America, sphagnum is called ‘sphagnum peat moss’ while in Britain it is more often ‘sphagnum peat’.

In Australia, a number of products containing different versions of these mosses are available and the names are confusing!!  While their garden properties are fairly similar, their environmental impacts are rather different, and if you want to tread lightly on the planet you need to read the labels carefully.

Peat Moss

This term seems to be used interchangeably with ‘Sphagnum Peat’.  We could only find one source where harvest is “sustainable”.  Otherwise it is probably obtained from deep in peat bogs.

Sphagnum Moss

Some suppliers use material from Canada or New Zealand where moss growing on top of the bog is picked by hand and then loaded into helicopters in an attempt to avoid damage to the bog.  In some cases it is claimed that the moss is “farmed”.  There are also products from New Zealand where harvesting is claimed to be sustainable.However, watch out for other products where there is NO information about the source material.

Blonde peat moss

There are at least 2 suppliers of blonde peat moss. It is a lighter colour than peat moss because it is sourced from the top 2 metres of the peat bog. There is no information about methods of harvesting, but material from this depth almost certainly required heavy machinery use with accompanying environmental damage.

Coir Peat – a Sustainable Alternative

This is not peat derived from sphagnum moss. Sometimes called ‘Coco Peat’ or ‘Coconut Coir’, it is fibre from between the outer shell of coconuts and the inner material used for food.  It has similar properties to sphagnum peat with respect water holding capacity, but may have higher levels of salts if they have not been previously extracted.  Its pH is closer to neutral so does not acidify soil as does sphagnum moss.

So, since coir is a renewable resource, does not endanger fragile environments or contribute to global warming, it is a much better alternative as a soil amendment than even ‘sustainably harvested’ sphagnum moss.

References

  1. Lim, Xiao Zhi  (2016).  Vast Peat Fires Threaten Health and Boost Global Warming (2016).  https://www.scientificamerican.com/article/vast-peat-fires-threaten-health-and-boost-global-warming/
  2. Tasmanian Government (2016).  Sphagnum Moss – Sustainable Use and Management. http://dpipwe.tas.gov.au/conservation/flora-of-tasmania/sphagnum-moss-sustainable-use-and-management

  One Response to “Should I Use Sphagnum or Peat Moss?”

  1. What a shocking state of affairs. The peat industry is wholly unsustainable and needs to be highly regulated. Coir peat and coconut based products do have transport miles as a consideration but need to replace peat until other local crops can be developed. This message is only slowly emerging and needs wide community understanding.

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